Abstract
Resistance expression controlled by resistance gene Xa-1 was investigated in adult plants of Kogyoku group rice cultivars after inoculation with bacterial group I isolates of X. campestris pv. oryzae. Kogyoku group cultivars with resistance gene Xa-1 showed symptomless type of resistance reaction to bacterial group I isolates irrespective of their aggressiveness. Periodical population study showed that there was distinct difference in growth patterns between compatible and incompatible isolates in the leaf tissues of cultivar Kogyoku. Compatible isolate T7147 of bacterial group II grew logarithmically and reached its maximum level above 108 cfu per inoculation site. In contrast, incompatible isolates T7174 and Q6808 of bacterial group I multiplied at a much lower rate than compatible T7147, and reached their maxima at less than 106 and 105 cfu per inoculation site, respectively. In Kogyoku, population levels of six isolates of bacterial group I 12 days after inoculation ranged approximately from 105 to 106 cfu per inoculation site. The degree of multiplication of isolates T7174 and Q6808 in nine Kogyoku group cultivars ranged approximately from 105 to 106 and 104 to 105 cfu per inoculation site, respectively, 12 days after inoculation.
